The invention is related to methods and systems of forming a core for a fire door. More particularly, the invention is related to methods and systems for forming a fire door core containing resin and vermiculite.
The use of fire doors in buildings is an important factor in avoiding injuries and loss of lives and in preventing property damage as a result of the door""s ability to impede the spread of fire. In the interest of public safety, standards have been set by governmental agencies, building code authorities and insurance companies for the installation and performance of door assemblies which retard the passage or spread of fire. Building codes require that fire-resistant door assemblies pass standard industry-wide tests that are an evaluation of the fire-resistant properties of the door assembly in relation to heat and flame for a specified duration.
The manufacturing of cores for fire doors has always presented one or more of several different problems. Some manufacturing methods and systems yield cores for fire doors that do not meet particular building codes or fire regulation specifications, or at least do not meet all of a variety of such regulations in the various jurisdictions in which they might be sold or used. Some methods and systems may be too time-consuming, have a higher than satisfactory failure rate, or are simply too expensive. As a result, fire doors may not be used as often as desirable.
Satisfactory fire door core manufacturing practices should produce a core having certain basic properties meeting standard industry-wide fire endurance tests, such as those in accordance with UL 10C (1998), NFPA 252 (1995), and UBC 7-2 (1997). In these tests, a doorframe and door (including the manufactured core) are exposed to intense heat such as that generated by fire in a burning building. Exemplary conditions of such tests involve exposing the door assembly to temperatures which progressively increase within the range of 2000xc2x0 F. for an exposure period up to 1xc2xd hours or more. However, some manufacturing methods and systems produce fire doors that suffer from spalling during such a fire test. The spalling incurred may reduce the original thickness of the fire door by as much as 30-40%.
Satisfactory manufacturing practices should also produce a core having good integrity during exposure to fire. The core must resist burning, melting, spalling, cracking, bursting or deteriorating in a way which would cause the temperature, on the side of the door not exposed to the fire, to rise to the extent that the combustible veneer on the unexposed side of the door burns or chars substantially. During exposure to heat, the core must also exhibit good dimensional stability. The core must remain relatively stable and resist warping or shrinking to the extent that it remains in contact with the banding (stiles and rails) around its perimeter. Separation from the banding can cause the combustible components to burn away prematurely, allowing fire to penetrate the opening. Additionally, the core must be resistant to heat transmission, such that the transfer of heat from the fire-exposed side of the door to the unexposed side is deterred. Otherwise, ignition and possible spread of fire may result from premature charring or burning of the combustible veneer of the unexposed side on the door.
Other than these fire and heat-resistant properties, core-manufacturing practices should produce cores having properties related to the manufacture, installation and service of fire doors. For example, the door core must have sufficient strength, yet be light enough in weight, to allow a fire door employing the core to be hung and used without becoming unattached from its mounting.
Fire door core manufacturing methods and systems should also have a relatively low manufacturing rejection rate, a relatively high production rate, and allow a core to be produced with a relatively low cost.
Those skilled in the art will recognize that there is a need for a method and system for producing a fire door core that is effective to retard the penetration and spread of fire or the transmission of heat. Further needs in the art are a method and system for producing a fire door which does not incur an unsatisfactory level of spalling during exposure to fire and/or later exposure to the flow of a water from a fire hose. Still further needs in the art are a method and a system for producing a relatively strong and durable fire door core that is sufficiently light to avoid the trouble and expense of special door frame structures on which to hang a fire door made from it. Still further needs in the art are a fire door core forming method and a fire door core forming system that have a low failure rate, a low overall cost, and a high production rate.
It is therefore a primary object of the invention to provide a method and system for forming a fire door core that meet these needs in the art. More particularly, it is an object to provide a method and system for forming fire door cores that are well suited for entry doors. Additionally, it is an object to provide a method and system for forming fire door cores and fire door support structures wherein the fire door cores have a density lower than that of the fire door support structures.
The inventor has discovered that these needs may be met by a method of forming a fire door core, comprising the following steps. A mixture of exfoliated vermiculite, resin, and hydraulic binder is deposited into a mold. The mold, and thereby the mixture, is transferred to a heated press. A predetermined pressure at a predetermined temperature for a predetermined period is applied to the mixture through the press in order to cause the mixture to harden into a slab. The hardened slab is removed from the mold. The slab is impregnated with water. The impregnated slab is dried to a predetermined moisture content. The slab may thereafter be formed into a core for use in a fire door. Hardened slabs of different densities may be produced by the inventive process. Thus, a hardened slab having a lower density may be used for the core of the fire door, and a hardened slab having a density higher than that of the core may be formed into support structures, such as stiles and rails. The hardened slab used for the support structures is preferably not impregnated with water. The support structures may be utilized with the fire door core in forming the fire door.
A door core forming system, according to another aspect of the invention, comprises a plurality of raw material sources, a mixing system, a plurality of molds, a vibratory assembly, a heated press, a water impregnation assembly, and a drying assembly. The mixing system is in communication with the raw material sources. Each mold is in operative communication with the mixing system for receiving a predetermined supply of mixed raw materials. The vibratory assembly is for receiving each of the molds and causing the mixed raw materials to achieve a substantially uniform density in each mold. The press is operatively associated with the vibratory assembly and is for receiving the filled molds and applying sufficient heat and pressure for a sufficient period to cause the mixed raw materials to achieve a slab having a hardened state. The water impregnation assembly is operatively associated with the press and is for impregnating the hardened slabs with water or steam. The drying assembly is operatively associated with the water impregnation assembly and is for drying the slabs to a predetermined moisture content. Different densities of hardened slabs may be simultaneously produced by the inventive system by utilizing a plurality of presses, each of which is adapted to produce a hardened slab of a particular density. Thus, a hardened slab having a lower density for use as a fire door core may be simultaneously formed along with hardened slabs having a higher density for use as fire door support structures, such as stiles and/or rails.